Bicozamycin benzoate is a substance known in the art (cf. e.g. Japanese Kokai Tokkyo Koho Sho 48-39497 and U.S. Pat. No. 3,923,790). It is currently on the market as a fishery drug and under development also as a veterinary drug. The process for producing bicozamycin benzoate as described in the above-cited patent specifications comprises reacting bicozamycin with benzoyl chloride. In said process, the selectivity of the esterification reaction is low and, as a result, the reaction product contains a significant amount of byproducts such as bicozamycin dibenzoate. For commercial production of the objective compound bicozamycin benzoate, said process is thus not fully satisfactory from the yield and production cost viewpoints.
For solving the above problems by attaining an increase in the yield of bicozamycin benzoate, among others, it is crucial to find out a way to increase the selectivity toward monoesterification.